In an electrically controlled throttle apparatus shown in FIG. 11, a driving device such as a motor controls an opening degree of a throttle valve 102 in accordance with a position of an accelerator pedal stepped by a driver. In the throttle apparatus, a gap is formed between an inner periphery of a substantially tubular throttle body 101 and an outer circumferential periphery of a throttle valve 102, and the gap has a large influence of an air tightness of the throttle apparatus when the throttle valve 102 is in its full close position.
Conventionally, the throttle body 101 and the throttle valve 102 are independently manufactured in each different process. Subsequently, a manufactured throttle valve 102 is combined with a manufactured throttle body 101 in accordance with an inner peripheral dimension of the manufactured throttle body 101 in a downstream process. Alternatively, a manufactured throttle body 101 is combined with a manufactured throttle valve 102 in accordance with an outer circumferential dimension of the throttle valve 102 in a downstream process. Thus, a predetermined gap is obtained between the bore inner periphery of the throttle body 101 and the outer circumferential periphery of a throttle valve 102. A throttle shaft 103 integrally rotates with the throttle valve 102. Both of the ends of the throttle shaft 103 are rotatably supported by cylindrical bearings 104 provided in the throttle body 101.
U.S. Pat. No. 5,304,336, which is a counterpart of JP-5-141540A, shows molding methods in which a manufacturing process of the throttle body and the throttle valve is reduced. In the molding methods, the throttle body 101 and the throttle valve 102 shown in FIG. 12 are integrally molded of a resinous material in the same molding dies. At first, the substantially tubular throttle body 101 is integrally molded of a resinous material. Subsequently, inner periphery (bore inner periphery) of the throttle body 101 is used as a part of a molding die molding the throttle valve 102, and the throttle valve 102 is molded. Thus, a shape of an outer circumferential periphery of the throttle valve 102 is adapted to a shape of the bore inner periphery of the throttle body 101 in the above molding methods.
The molded throttle body 101 is gradually cooled in the body cavity to be solidified. Subsequently, the movable die is slid forward in order to form a valve cavity, into which a resinous material is filled. The throttle valve 102 is molded of a resinous material in the throttle body 101.
However, in the above molding methods of the throttle valve 102, the throttle body 101 is molded of a resinous material while the molded throttle body 101 is restricted by dies in its radial direction and in its substantially circumferential direction. Thus, the throttle valve 102 is molded of a resinous material while the throttle body 101 and the throttle valve 102 are restricted by the dies. The throttle body 101 and the throttle valve 102 are taken out of the dies, and gradually cooled. In this cooling period, the unrestricted throttle body 101 and the throttle valve 102 are contracted. The throttle body 101 and the throttle valve 102 are deformed. Accordingly, it is difficult to maintain the gap in a predetermined dimension between the inner periphery of the throttle body 101 and the outer circumferential periphery of the throttle valve 102.
A practical use of the throttle apparatus releases an internal stress, by which the apparatus is deformed. When the throttle apparatus is made from a crystal resin and is crystallized, the apparatus is deformed due to the crystallization thereof. Even the apparatus is annealed or aged, the throttle body 101 and the throttle valve 102 are deformed individually,
To solve the above problem, the inventors filed Japanese patent application No. 2003-285434 on Aug. 1, 2003. In this application, the throttle valve and throttle body is formed in a same die in such a manner that the throttle valve is opened in a predetermined angle. However, as shown in FIGS. 13, and 14A, when a valve gate through which a melted resin is injected into cavity is located at an outer periphery of the throttle valve 102, the throttle shaft (a metal shaft) 103 is deformed by an injection pressure of the resin as shown in FIG. 14B. In FIGS. 13, 14A, 14B, a direction of resin injection is represented by an arrow. When a valve gate is located at the throttle shaft 103 and a melted resin is injected in a direction which is perpendicular to a radius direction of the throttle valve 102 as represented by an arrow, the throttle shaft (the metal shaft) 103 is deformed as shown in FIG. 16B.
As mentioned above, when the melted resin is injected into the cavity from the valve gate located at the non-symmetry position with respective to the throttle shaft 103, the throttle valve 102 cannot rotate smoothly in the throttle body 101. Alternatively, the circularity of the throttle valve 102 is deteriorated. Thus, when the throttle valve 102 closes the throttle body 101, a clearance between the inner surface of the throttle body 101 and the outer surface of the throttle valve 102 becomes large to increase an air leakage therebetween.